Conventionally, there has been a known card edge connector which connects a daughter board such as a memory module to a printed circuit board as a mother board incorporated in equipment such as a personal computer. For example, Japanese Patent Application Publication No. 2002-190354 describes a card edge connector having an insulation housing mounted on a mother board and a pair of latch arms mounted on the housing which holds a daughter board. The latch arms are formed by stamping and bending a metal plate. The latch arms hold the daughter board utilizing its own elasticity.
In recent years, it has been known to connect a plurality of daughter boards to a mother board. For example, to increase the memory capacity of a personal computer, it is known to connect a plurality of memory modules to a mother board. On the other hand, in the case of equipment which is required to be reduced in size, it is desired to reduce the amount of space occupied by the memory module connected to the mother board.
For example, U.S. Pat. No. 6,126,472 describes a connector assembly including an edge connector having a resin latch arm which is integrally molded together with a housing. The connector assembly includes an upper card edge connector and a lower card edge connector. Both the upper card edge connector and the lower card edge connector include a housing which receives from a front thereof a dual inline memory module (DIMM) as a daughter board and passages that extend forward from both sides of the housing. The upper card edge connector is at a position lifted up by a lifting member, and the passages are superposed on the lower card edge connector and positioned rearward. Therefore, the DIMM received by the upper card edge connector is superposed on the lower card edge connector and the area occupied on the mother board is small.
FIGS. 1(a)-(b) show another conventional example of card edge connectors having metal latch arms wherein two daughter boards D1, D2 can be disposed such that they are superposed on each other. In FIGS. 1(a)-(b), the two card edge connectors can be used as one set or can be used independently from each other. As shown in FIGS. 1(a)-(b), the lower card edge connector 1 and the upper card edge connector 2 are mounted on a mother board M, and memory modules, as daughter boards D1, D2, both having the same shapes are attached to the lower card edge connector 1 and the upper card edge connector 2. In the following description, a side of the mother board M is defined as down D, its opposite side is defined as up U, a side where the daughter board D1, D2 is received is defined as front F, its opposite side is defined as back B, right moving forward from is defined as right R, and left side is defined as left L.
First, a structure which is common for the lower card edge connector 1 and the upper card edge connector 2 will be described collectively. The lower card edge connector 1 and the upper card edge connector 2 respectively include insulating housings 11, 21 that receive daughter boards D1, D2, a plurality of contacts 12, 22, a pair of latch arms 13, and a pair of latch arms 23. The insulating housings 11, 21 are provided with daughter board receiving recesses 111, 211 that receive the daughter boards D1, D2 from the front F. The contacts 12, 22 are disposed along a longitudinal direction of the daughter board receiving recesses 111, 211 (only a few of the contacts 12, 22 are shown). The latch arms 13, 23 project forward F from both left and right ends in the longitudinal direction of the insulating housings 11, 21, i.e., in the lateral direction. The latch arms 13, 23 are formed in a bilateral symmetrical manner wherein left and right structures thereof are in common.
The latch arms 13, 23 include holding arms 131, 231 which support the daughter boards D1, D2, support arms 133, 233 which support the holding arms 131, 231, folded portions 132, 232 folded back from the holding arms 131, 231, and press-fit sections 135, 235 which are press-fitted into the insulating housings 11, 21. Each of the latch arms 13, 23 is formed by stamping and bending one metal plate. That is, the holding arm 131, the support arm 133, the folded portion 132 and the press-fit section 135 are integrally formed together, and the holding arm 231, the support arm 233, the folded portion 232 and the press-fit section 235 are integrally formed together. The holding arms 131, 231 and the support arms 133, 233 are bifurcated through the folded portions 132, 232, and the press-fit sections 135, 235 located at root sides of the bifurcated portions are fixed to the insulating housings 11, 21.
The holding arms 131, 231 extend forward F, and the folded portions 132, 232 are folded back outward by about 180 degrees from upper edges of rear ends of the holding arms 131, 231. The support arms 133, 233 extend forward from the folded portions 132, 232. The fixed sections 134, 234 project from lower edges of the support arms 133, 233. Mother board attachment members 15, 25 soldered to the mother board M are mounted on the fixed sections 134, 234. The press-fit sections 135, 235 extend backward B from the support arms 133, 233. The holding arms 131, 231 are provided at tip ends with first locking members 131a, 231a which are engaged with notches formed in the daughter board D1, D2, and second locking members 131b, 231b which prevent the daughter board D1, D2 from floating up and coming out from the first locking members 131a, 231a. 
The press-fit sections 135, 235 of the latch arms 13, 23 are press-fitted into the insulating housings 11, 21. The holding arms 131, 231 are supported by the insulating housings 11, 21 in a cantilever spring manner through the press-fit sections 135, 235 and the folded portions 132, 232. The holding arms 131, 231 themselves are elastically deformed so that tip ends thereof are displaced in the lateral direction LR. When the daughter boards D1, D2 are attached to the lower card edge connector 1 and the upper card edge connector 2, the holding arms 131, 231 are once elastically deformed outward by manual operation. After the edges of the daughter boards D1, D2 are received by the insulating housings 11, 21, the holding arms 131, 231 return inward and the holding arms 131, 231 sandwich the daughter boards D1, D2 from both end edges in the lateral direction LR by their elasticity. The first locking members 131a, 231a of the holding arms 131, 231 are engaged with edges of the daughter boards D1, D2.
The support arms 133, 233 are formed with inclined portions 133a, 233a which bend at positions in front of front edges of the folded portions. The inclined portions 133a, 233a are inclined forward and diagonally outward. The support arms 133, 233 are again bent at positions forward F of the inclined portions 133a, 233a and extend forward substantially in parallel to the holding arms 131, 231. A stopper 133c is provided on a tip end of the support arm 133 of the lower card edge connector 1 to prevent the holding arm 131 from being bent excessively. In addition, a pair of stoppers 233b, 233c is provided on a tip end of the support arm 233 of the upper card edge connector 2 to prevent the holding arm 231 from being bent excessively. The holding arm 231 is disposed between the stoppers 233b, 233c. Further, the fixed sections 134, 234 project from lower edges of tip ends of the support arms 133, 233. The fixed sections 134, 234 extend in the lateral direction LR. The mother board attachment members 15, 25 are arranged on the fixed sections 134, 234.
The lengths of the holding arms 131, 231 of the latch arms 13, 23 are determined in accordance with the size specifications of a daughter board D1, D2 to be attached. A force required for deforming the holding arms 131, 231 outward, and forces of the holding arms 131, 231 for pinching the daughter board D1, D2 are determined by the lengths of the folded portions 132, 232. Portions of the holding arms 131, 231 which are provided at their upper edges in the folded portions 132, 232 have higher rigidity as compared with other portions of the holding arms 131, 231 which do not have the folded portions 132, 232. The holding arms 131, 231 are in communication with the support arms 133, 233 to be fixed to the mother board M and the insulating housings 11, 21 through the press-fit sections 135, 235 and the fixed sections 134 and 234 by the folded portions 132, 232. As the lengths of the folded portions 132, 232 are longer, the rigidities of the entirety of the holding arms 131, 231 are higher. The lengths of the folded portions 132, 232 of the lower card edge connector 1 and the upper card edge connector 2 shown in FIG. 1 are adjusted to such a level that the holding arms 131, 231 can appropriately be bent outward with finger's force and the daughter board D1, D2 is pinched between the holding arms 131, 231 with such a force that the daughter board D1, D2 is not pulled out.
Next, a difference between the lower card edge connector 1 and the upper card edge connector 2 will be described. The height of the insulating housing 21 of the upper card edge connector 2 is about two times of that of the insulating housing 11 of the lower card edge connector 1. The daughter board receiving recess 211 is formed at a position twice as high as the daughter board receiving recess 111 of the lower card edge connector 1 as measured from the mother board M. The holding arm 231 of the upper card edge connector 2 is disposed at the same height as the daughter board receiving recess 211.
As shown in FIG. 3, the support arm 233 of the upper card edge connector 2 is about two times as high as the support arm 133 of the lower card edge connector 1 in accordance with the height of the insulating housing 21. The fixed section 134 of the lower card edge connector 1 is bent inward, but the fixed section 234 of the upper card edge connector 2 is bent outward. Therefore, the lower card edge connector 1 can be disposed between the pair of the latch arms 23 in front of the inclined portion 233a of the upper card edge connector 2.
As shown in FIG. 4, the lower card edge connector 1 and the upper card edge connector 2 are mounted on a surface of the mother board M by soldering. The insulating housing 11 of the lower card edge connector 1 is disposed between the pair of the latch arms 23 of the upper card edge connector 2 on the mother board M. The latch arms 13 and the latch arms 23 are press fitted in both ends of the insulating housings 11, 21 in the lateral direction LR, and the insulating housing 21 of the upper card edge connector 2 has the same length as that of the insulating housing 11 of the lower card edge connector 1 in the lateral direction LR. The insulating housing 11 of the lower card edge connector 1 is disposed in front of the inclined portion 233a formed on the latch arm 23.
In a state where the daughter boards D1, D2 are mounted on the lower card edge connector 1 and the upper card edge connector 2, the insulating housing 11 of the lower card edge connector 1 and a portion of the daughter board D1 mounted on the lower card edge connector 1 are superposed on the daughter board D2 mounted on the upper card edge connector 2, as viewed from above. Therefore, according to the lower card edge connector 1 and the upper card edge connector 2 shown in FIG. 4, the occupied area on the mother board M is reduced by the superposed portion as compared with a case in which the daughter board D1, D2 and the lower card edge connector 1 and the upper card edge connector 2 are not superposed on each other and the mother board M can be utilized effectively.
In recent years, as can be seen in notebook personal computer, it is required that an area of a mother board M occupied by a part is further reduced as the equipment is reduced in size and the performance thereof becomes high. In a connector to which the daughter board is attached, it is also required to increase an area of superposed portion and to reduce an area occupied by the connector. In the lower card edge connector 1 and the upper card edge connector 2 shown in FIG. 4, if a disposition distance W1 between the lower card edge connector 1 and the upper card edge connector 2 is reduced, the area of the superposed portion is increased. As a method for reducing the disposition distance W1 between the lower card edge connector 1 and the upper card edge connector 2, it is conceivable to shorten the length of the folded portion 232 in the upper card edge connector 2, and to form the inclined portion 233a rearward B as compared with the position shown in FIG. 4, i.e., closer to the insulating housing 21.
However, if the length of the folded portion 232 is changed, the rigidity of the holding arm 231 is changed. That is, if the folded portion 232 is shortened, there is an adverse possibility that the folded portion 232 can not hold the daughter board D1, D2. In addition, the folded portion 232 connects the holding arm 231 and the support arm 233 to each other. Thus, if the length of the folded portion 232 is shortened, there is a possibility that the folded portion 232 is damaged when an excessive force is applied to the holding arm 231 or when a force is repeatedly applied.